Method and structure for processing an electron discharge device



Patented May 23, 1950 Section 1, Public m wsesomugust -s, 1946 -Patent'-expires September- 12;1961

The presentinvention relates to electrondischarg e devices of thek-ind havingfa screen 'and in which `atsome stage` during the manufacture o' lifeof the-dvice it isdesiredtb carry. o'it a. treatment with a gas or vapour 'which is releasedihepresence of said screen and becomes distributed 'through the envelop'e 'o'f the device, 'said gasor Vapour being nxious in re. sp'otofsaidiscreen. 3

'Thelnvention has beehdeveloped 'in connection. with an. eleotron dischar'ge device' known as a,..picture transfbrmer comp'sing. a photocathodea-nd a 'fliorescen't screen dis'pbse'd within. an. envelope so. that if an p'tial 'imageis focusseclon tothe cathode it causesgthe einissi'on therefrom of `photo -electrons, .ancl t'he ccmpos'it'e beam dfelectrons thus obtainedisprojectedon tc thefluorescent screen and the image isvrep'roducedthereon. In 'the constructionof such a devicev-it 'is usual after the fiuorescent screen has been inserted within th envelope to ;form a photo-cathode byevaporatinga suitable founda'- tion -on 'to a member; which may, for example, abe part of the envelope, and` then treating 'the:- foundation by admitting oxygen: and caesium: vapour after evacuationei' the envelope. Thse operations may, however, .result in `damage `tothe: fluorescent screenif -it 'is not protected; various expedients-have already been proposed for af fording protection to the fiuorescent screen, -in-- volvingforexample, the use` of protective -fia ps support member, holi'ng means for: ma iitainngi .e rangement 'being i such 'that' said support mem:-

for coveringv the.. finorescent ,i screen during the formatiomof .the -.oathode. or the makingm, the` cathodevreversbl-p T he se of a flapis not ena m y. satisfactory. wlere th y cathod and screen are requiredto operate in close proximity, as it i difllt to accommodate theanto` p re- ?exit 'undesiredi elec'trical discha-r'ges occurring betweenlhe cathode e and l the fiap. Alsmwhere it. is .required Ito form the cathode on i an m mov'abl member such as !a 'window iorming part of .the want: the envelope, ..itis not possible-to makethe cathodereversible. e 'The obj ect -oi the present invention is to afford lii'tctin 'fr 'said `screen while tl'e treat-- ment. with .ioxious gaso'r v'rpour is being carijid-"dutwithout-the necessity of employing a flito ?protect .the screen. and without 'the .neces-. ity of empoyi ga 'rvei'ldl c'athoder According toft'he present invention there is provided--an ere'ctrbn' vdisoharge dvice or a iie Vice for. 'use in .the :manufacture of. an. electron dischange s device, saidi device eomprising a. subt'ahtally closed .en e1op-a movable support memb r carryin a .sfen gr. m'otifimgflfor' Said in ,said envelope in which position ;s'aidsoreen sandwiched between said supportmember anila? further member so as to be unexpq'sed wherehy damage to'saic l screen b'ygaspr vapiri'ocii to said screen whih ma lde 'adnttedtb said eh:-

velop in the presence ofsaidscreen dringip ubsequentlto manuac'ture can be substantially avoided, a n& said 'support'member can then 15' caused to from said safe 'positidh 'intsaid mounting. and into said' Operating position by. manipulation of said dvice. Prefera'ply, S' do' holdifgmeans a i'e arl'ahgd to b opi'bl foli without saidrenvelope to allow au qppcrtmmg ber to. be released *rr m said mintifig after d; support 'member ha's 'been iont'd i'd ig bysad holdingmeans.- f

. The iVen'tion further includsthe itlod of manufoturingan eletron disbh'rgfe dfiice, and anelectron dschalrgdvice mifaotr by said method, emplcsiih gfa 'd''ice m ceorac with 'the inventibnand comiarising 'mambiIating.;.`the-device 'to causeth'e 's pprtember 'i'of the screen to mve toits sae bo s fiibmaadntting. or releasing a vapour or gas which noi:: ious in respect o'fthesreer so a's toitreat an ele mentof saiddevicewithin the envelopeandsub sequently causing said support member to fimove to its Operating position. I

Inorder that the a-id inventionmay beclearly nderstood and readilycarried into efiect. it wll now be more fu l lydescribed with refrnce to the accompanying. drawings, inwhich:

Figure 1 is --a side e'levational View, partI y in` section, of anelectron discharge devicein the form of a picture transformer c'ontruc ted in accordancewiththe invention,. i

Figure 2 is =a detail view showingi-n front elevatio'n the frame bywhich ?the hiorescentscreen:

and'the silver eva'porators or providing-the siv t base for :the photo-cathode aremountel on the headerof the device shown mFigure and;

Figur 3 is 'a det'ail top planyietv showin t ;h screen and 'screencatch in the device of Ffgure l withjthe front andipper members of the=a fore said frame. I Referring ..to Figure 1 of the draw-ingit-'w11l beseen-that the deVCe-thereinshO n comprises; i les& lq r' cq s fa Gl d 'fl laving, oneend-'closed by an. end ,wall-& aad;

other end sealed by a disc-shaped header 4 which is inserted within the end of the cylinder 2. The end wall 3 and the header 4 are each formed so as to provide a window, both faces of each being optically worked. On the inner face of the end wall 3 is formed the photo-cathode 5 which is illuminated through the end wall. The fluorescent screen 6 is formed on a support memin the ring IS by means of a bracing wire 24,

ber constituted by a glass disc 'I carried ina' mountin 8 supported on the header 4, the screen 5 being viewed through the header 4. E The Construction of the mounting 8 is described more in detail below. The screen 6 is shown formed in which engages'the disc 1 near the edge thereof, and a catch 25 which engages the edge of the disc 1 at a point diametrically opposite the middle of the wire 24. The wire 24 may be iormed of Figure 1 facing away from the cathode, but in` operation the screen 6 is arranged to face the cathode and to extend parallel thereto and sepa-.

rated therefrom by a gap only a few millimetres wide.

The envelope I is evacuated through an aper- I ture 9 in the wall of the cylinder 2. The photocathode 5 is formed in the manner described in British Patent specification No. 492,()36, that is to say, the photo-cathode is formed by depositing a' thin layer of silver on the glass wall 3, this layer being oxidised and a' relatively thick layer of silver being applied over the oxidised layer to render it conducting and the oxidised layer being rendered light-sensitive by treatment with caesium vapour before or after the deposition of the relatively thick layer. The silver ior forming the cathode is furnished from two evaporators ll each comprising a silver-coated heating filamen't and a cylindrical shield having an opening'through which the silver vapour is ejected. The evaporators ll arecarried on the ends of arms !2 forming part of the mounting 8, while caesium vapour is admitted through the aperture !3 in the wall of the cylinder 2, the aperture !3 being preferably disposed at the end of a diameter at right angles to the corresponding diameter through aperture 9.

, Electrical connection to the cathode 5 is affected through a lead-in wire M, for example, of

tungsten, passing through the wall oi the cylin-- der 2 and a strip of burnished silver !5 painted on the'inside of the cylinder 2 and end wall 3.

The mounting 8 carrying-the disc 1 on which the fluorescent screen 6 is formed comprises two side rods ll and !8 which may be formed of tungsten andare sealed through the header 4 at diametrically opposed points. An arm |2 is Secured to each of the rods l'l and 18 at a point near to the header -4, the arms [2 and evaporators Il iorming a complete hoop girdling the support rods. The arms `i2 are insulated from the shields of the evaporatrabut are electrically connected through the heatingfilaments thereof so that the rods l'! and !8 constitute lead-in wires for the evaporator heater currents. The mounting 8 is completed by bezel ring [9 of J or L-iorm crosssection which may be formed of nickel, into which the disc 'I ts. The ring !9 has wires 28 welded on to it registering with the rods l'! and !8 respectively, the wire 20 shown uppermost in Fi ures 1 and 2 being Secured to the rod ll by means of a tight fitting metal sleeve 2l which is welded to wire 28 and rod IT to provide an electrically conducting connection between the ring !9 and the rodl'l, while the lowermost wire 20 is secured to rod !8 by means of a bead 22 of insulating material, such as glass.

The screen 6 is formed of willemite or similar uorescent material deposited on a platinum gi'aticul'e which provides an electrically-conducting backing for the screen, the graticule-being nickel and is welded on the ring |9 while the catch 25 is formed of a material, such as Permalloy, and is supported on a spring 26, formed of tungstem. for example, carried by a clip 21 mounted on the rod IT. The spring 26 is biassed inwardly and forces the catch 25 through a cutout portion 28 (see Figure 3) in ring s, against the disc 'i which is thereby rmly gripped in position. The front edge 29 of catch 25 is preferably slightly inclined so that the catch 25 exerts a wedging action on the disc 1 and tends to bind more and more tightly if the-device is subject to vibration.

As indicated above, the frame 8 'is assembled on the header 4 with the disc 1 disposed in the ring !9 with the screen B presented to the header 4. The header assembly is then inserted and sealed in the `cylindrical portion 2. At this stage the screen 6 must be moved to a position of safety where it will not be subject to action of any vapour or gas released during the formation and treatment of the cathode 5; To cause the screen 6 to move to the aforesaid position of` safety the device is supported with its'end wall 3 uppermost and the catch 25 is disengaged from the disc 'I by applying a magnet outside the oylinder 2 to cause the catch to move against the action of the spring 26. The disc 'I then drops down'and by gentle manipulation of the device the disc may be caused to fall to the position indicated in dotted lines at 'I' in Figure 1, where the disc lies flat on the header 4 with the screen 6 sandwiched between the disc and the header, the exposed surface of the screen, that is to say the surface of the screen liable to be attacked by noxious vapour or gas, being covered by the header. The screen 6 is thus completely protected.

After the disc 'I and screen 6 have thus been moved the envelope is sealed onto the pumps and evacuated; heater current is supplied to the evaporators II, through rods I'l and |8 and arms !2 to liberate silver vapour as required during the formation of the cathode 5, oxygen is'admitted to oxidise the cathode and excess pumped off; and then the caesiumvapour for sensitising the cathode is intrcduced through aperture 13. When the formation and sensitising of the cathode is completed, the lead-in tubes connected to apertures 9 and !3 are sealed ofi and the disc 'I can then be caused to move into the operative position with' screen B presented to the cathode 5. To bring about this movement the device is rocked so as to cause the disc 1' to fail from the position 'i' into the position shown dotted at 'I" in' Figure 1, with a swinging movement, as indicated by the arrow 30, and is further rocked to cause the disc to Swing in a direction indicated by the arrow SI so that the disc 'I falls on to thebezel ring s again, but with the screen 6 presented towards the cathode 5 and with the bottom of the disc gently engagedby the wire' 24 which serves to, guide the disc intoposition in the ring IS so that' when the 'catch 2 5 i's withdrawn eme agai'n, the disc 1 is permitted to mov'to `its-operative position'w ith thescrehfi rest'ng 'on'the inner edge of the bezel. The catch 2 5-i`s thenre'leased and oeks the disc J fi-mly in position 'If-,for any reason, it is'required to 're-treat the cathode 5 it will be seenjth'at the disc'l and the screen TE can be 'movedto a position of safety whenever 'desiredby` simply withdr'awing catch ana suitably m anipulatiag thje-device. r

It willbe seen 'that with the 'arrangement described indetail 'above the fiuoi escent screen 6 can be moved to a 'position ofsafety freely and without damag'e Phis enables the screen 6 to be brought, 'inopertiom ascldse to the cathode 5 as desired, thus -simpli f n'gthe focussing of -electrons'from the eatho'd on to the screen. In cases where the cathede'an'd screenop'erat'e-in Very close proxim-itr-it is desi'i able to provide means for preventing undesired dischar g s tal i r g place between the 'screen and the *athode It is found that a e'oati'g` *of conducting material, for example, a suspension of 'colloidal gr'aphite applied round the 'outside of the cylinder *2 'in "the vicinity of the cathode, as -indicated at '32 in Figure 1, and

maintained at 'approxi'matly oathode potential when 'the 'device is oper'tion -is 'effective to prevent these disch argsoccurring.

What Icl-aim is:

1-. 'An le'ctron dischai ge devicecomprising an envelope, a mmbe1' mouht in position within said envelope, a coatmg 'on o'e face of saidmember, said r-'veepe navin an inner surface conforming With said coated racizmi said member., releasablemeans within said envelope for looking said member in mounted position and for releasing said member whereby said member may be positioned with said coated face in contact Withsaid inner envelope surface.

2. An electron discharge device comprising an envelope, a plate member mounted in position within said envelope, an activated material coating one 'face of said plate member, said envelope having a'n 'inner surface cofforining with the coated -face of said 'plate member, releasable means within'said 'envelope for looking said plate member in in'ounte'dp'osition and for releasing said plate whereby 'sa-id plate may be positioned with said coated face in contact with said inner envelope surface.

An electron discharge device comprising an envelope, a screen mounted in position within said envelope, said screen having a surface portion thereof coated with an activated material, said envelope having an inner surface unobstructedly spaced from said screen, said inner envelope surface conforming with said coated surface portion, means within said envelope for releasably holding said screen in mounted position, said holding means including a movable catch for releasing said screen from the mounted position whereby said screen may be positioned with said coated surface portion in contact with said inner envelope surface.

4. An electron discharge device comprising an envelope, a member mounted in position within said envelope, said member having a sensitized surface thereof, a header element forming a part of the wall of said envelope, said header element unobstructedly spaced from said member, a portion of the inner surface of said header conforming with said sensitized surface of said member, releasable means within said envelope for holding said member in mounted position and for be* positoned with 'said srisitied surfae in `com tact with said conforming inner surfade `portion of said header.

5. An electron discharge device r'c'omprising a tubular envelope, a header element 'closing one end of said: envelope, ascreen within :said envelope 'mounted on said 'header element, 'said header having a portion 'of the n'clos'edsurface thereof unobstructedly `spaced from said screen, said screen having -'a.sensitized surface,said por tion of the en'close'd surface of -said header con-- forming with said sensitized surface of said screen, releasable 'means within .said envelope forholding said screen in :mounted position and -for re'- leasing said screen 'whereby :s'aidsc r een may be positioned With said sensiti'zed surface in contact with said conformingsurfac portion (if-said header.

6. An 'electron 'discharge device comprisin g a tubular envelope, a'header di'sc seale'd to one end' of said envelope, "a screen within said envelope, means fixed to saidiheader disa for supporting said 'screen in a .position unobstructedly sp'aced' from said header disc, said. screen having a s'ensitized surface, a portion of the innersurface of' said header disc conformi-ng with said sensitized screen surface, a mova'ble catch mounted on said screen supporting mear'sfor hoidin g said screen in said unobstructed .posi-tion and for re-, leasing said screen whereby sai'd screen be positioned with said sensitized surface in 'contact: With sad-conorm-in g inner surface meam-.header.

7. An electron 'dischar'ge device "comprising` 'a tubular envelope, an end wail closingone 'end of said envelope, a. header disc 'seale'd across, the other end of said envelope, aplatemember Within said envelope, one-face of said plate'member being sensitized means mountedon said header disc for supportingsaidplat'e member inva posi:- tion unobstructedly -spaced between, said header disc and said end Wail, a .portion of the inner surface of. said header disccnformi-ng With said sensltzed face, of said ;plate mmbenreleasable means on said plat'e member'supportingmeans for holdings said plate 'member in said un'obstructed posi-tion 'and for releasi ng said pi ate member, whereby said piate "membermay be .positioned with said 'sensitized face contact With said conforming inner surface 'of said headez 8. An eiectron 'discha-rge device comprising' a tubular envelope, an end wall adapted to be sensitized closihg one end of said envelope, a header member sealed to the other end of said envelope a support plate within said enevelope, an activated material coating one face of said support plate, means fixed to said header member for mountng said support plate in a position unobstructediy spaced between said header mem-- ber and said end wall, a portion of the inner surface oi' said header conforming With said coated face of said support plate, releasable means on said support plate mounting means for holding said support plate in said unobstructed position and for releasing said support plate whereby said support plate may be positioned With said sensitized face in contact with said conforming inner surface of said header during formation of a sensitized surface on said end wall.

9. A header assembly for scaling to an electron discharge device, said assembly comprising a fiat header disc, supporting means fixed to said header disc, a sensitized screen mounted in position on said supporting means, releasable means releasing said member whereby said member may fixed to said supporting means for holding said acomc screen in position and for releasing said screen from said supporting means.

10. A header assembly for an electron discharge device having an envelope, said assembly comprising a fiat header member for closing said envelope, supporting means fixed to said header member and extending from one face thereof, a screen mounted on said supporting means and unobstructedly spaced from said header member, a sensitized coating on one portion of said screen, said one face of said header member conforming with said coated portion of said screen, releasable means on said supporting means for holding said screen in said unobstructed position and for releasing said screen whereby said coated portion may be positioned in :contact with said conforming face of said header.

11. A header assembly for an electron discharge device having an envelope and a photocathode, said assembly comprising a flat header member for closing said envelope, supporting means fixed to said header member and extending from one face thereof, a screen mounted on said supporting means, said screen having a sensitized surface, means fixed to said supporting means for forming said photocathode, said one face of said header member conorming to said sensitized surface, said supporting means including a releasable catch for holding said screen in mounted position and for releasing said screen whereby said screen may be positioned with said sensitized surface in contact with said conforming face of said header member during ormation of said photocathode.

12. A header assembly for an electron discharge device having an envelope, said assembly comprising a header member for closing said envelope, a supporting frame fixed to said header member and extending from one face thereof, a screen mounted on said frame and unobstructedly spaced from said header member, a fluorescent coating on one surface of said screen, said one face of said header member conforming to said fiuorescent coated screen surface, means fixed on said supporting frame for evaporating a meta] photocathode layer on the inner surface of said envelope, sai'd supporting frame including releasable means for holding said screen in mounted position and for releasing said screen whereby said fluorescent coated surface may be positioned in contact with said conforming face of said header during formation of said photocathode.

13. An electron discharge device comprising an envelope, :a header member forming part of said envelope wall, a screen within said envelope, supporting means fixed to said header and enclosed within said envelope for mounting said screen in position adjacent the inner surface of a portion of said envelope wall, said screen having a sensitized surface, a metal evaporator fixed to said supporting means for forming a photocathode layer on said inner envelope surface portion, said header having an enclosed surface conforming with said sensitzed screen surface, said supporting means including -a releasable catch for holding said screen in position adjacent said wall portion and to release said screen whereby said sensitized surface may be positioned in contact With said conforming header surface during formation of said photocathode layer.

14. An electron discharge device comprislng an envelope, a header member forming part of said envelope wall, a screen within said envelope, said screen having a sensitized surface, a metal evaporator mounted within said envelope for forming a photocathode layer within said envelope, said header having a surface enclosed within said envelope conforming with said sensitized screen surface, releasable means within said envelope for maintaining said screen in one position and for releasing said screen from said position whereby said sensitized surface may be positioned in contact with said conforming header surface during formation of said photocathode layer.

HARRY CASSMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,917,855 Rentschler July 11, 1933 2,283,413 Cashman May 19, 1942 2374287 Henry Apr. 24, 1945 2,411,046 Liimatainen Nov. 12, 1946 FOREIGN PATENTS Number Country Date 501,270 Great Britain Feb. 23, 1939 

